What quantity is measured by a battery rating given in ampere-hours q y8za-7 8hz di36y 7wh1c gsejelvz15$(A\cdot H)$ ?

When an electric cell is connected to a circuit,upqz-m.9,2d5l skrohlx vu :10jd e:g electrons flow away from the negative terminal in the circuit. But within the cell, ox 1s92-jvplqezr ,gl.k0:muddhu5 :electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being uja2 ::ol x bxr8ybxdtyi4k+ --sed up: battery current, battery voltage, battery energy, battery power, or battery resi4l :t:ayix+bjk2-xd o8rb -yxstance? Explain.

One terminal of a car battery is sa 5-8*dyshop.i 1 0/iygvru vaeid to be connected to “ground.” Since it is not really connected to the ground, what is meantpi5rigvo 8sd-y*1 .h e/ 0vyua by this expression?

When you turn on a water faucet, the water usually flows immed69n itx; *b1mjiakdl3iately. You don’t have to wait for water to flow from the faucet valve to the spout. *nl1xdt ;kbji9 3i6maWhy not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resi+)ji 6o o z8peuk,ah -nnym6n)stance? Expl 6aki6+phe)y -,ojm)8n nnz uoain.

If the resistance of a small immersioncdcjk,/r +/ cva6 h-i z6o5arx heater (to heat water for tea or soup, Fig. 18–32) was increased, wor ad-5h /j6ia6zxc r+/okc,vculd it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, ane fgz:1 hw6v mvksb vu.32fj(:d 3a, how would you connect the wires from a battery so awj6(zgv.:sv3bf 2fm e vh :1uks to obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb buresx* f,(d 5 g2 xrowjjemt**z8ns out?

Explain why lightbulbs almost always b:7-v3xc bosaa8w o5gtox 7 h,surn out just as they are turned on and not after tbsho,vog c 3 -7a:7a5sx8to wxhey have been on for some time.

Which draws more current, a 100-W lightbulb gqec :;v47mn6uar5xf or a 75-W bulb? Which has the higher resis54ua:v f mcgxn7 q6er;tance?

Electric power is transferred over large distances ewegs g)c8*thg 2 ha/-at very high voltages. Explain how te-/ ggt)ch w8ehsag*2 he high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse0 / ebvtt((o fgup-z 6iqocxw72lin(; with a 25-70n/lzo; ef (p2-t6 ub oqctiwg x(iv(A fuse?

When electric lights are operated on low-frequejfi0 3vo iw76n vyu4*sncy ac (say, 5 Hz), they flicker noticeably. ywoj3 7iv 46si0fn u*vWhy?

Driven by ac power, the same electrons pass backa .cpfk;1 lpk2 and forth through your reading 1kklp a f;.pc2lamp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately aft64zxbn2 7qtq *i*biweer the toaster is turned oint 2q*qxb*e6wz b4i7 n, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistj b3xw jsi4 4h.5weyh30grrb/;x9l wtor? Explain.

Different lamps might 3f4gu)a pzyzvn eydy0/.-b g,,, yomwhave batteries connected in either of the two arrangementsd.voa-bw e,z4y,/yzy, 0 u3mg )pfyg n shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows igrjy w: jjf5(0e5 k)cvn a wire. How many electrons are flowing past any point in the wire per jgjwvjr5(ck0)5 fy:e second?    $ \times10^{18 }\;electrons/s$

  A service station charges a batter+6m hcmr9jx/ yfk7qy :y using a current of 6.7 A for 5.0 h. How much cha+76jmx:hkr/ cqy f 9myrge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes inlh 0x4dui ,nbx .6i(gf $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a*lxep qvf53k(a 07xuq toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of currs l9nm 73j:osgent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluv 5foi1mi9 m*f pp5m- j8gn1eugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a h-sbz uzeum0 8:eating element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resi/ 2dzpd6ylff+zy 2)gugxkp/ m*n8u s,stance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmissio; x+m 5h8ewjrwn line carrying 2800 A (Fig. 18–34). The;5w+jxm 8rhwe line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240 V. c3 , )2-typmreiisukm:87ass
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of84 p*30lz p.zthbc*5cza uzkx 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of t41pik 9,.o/d vkwwkyu3 v sqc:gtpe,;ungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of /fv w06wzte4r; se8af-vi .hxa 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resijaakign ,7mb h l 7sg-1p.0n.fstance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 ,iap.0 fmbggnsan hk-l7 j71 .m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance asj5w;:b oszk 2-t6ol5r fhqsh hhqp:;: a tungsten wire of the same length? Goht 2 l::6zos br;5 h:k w5;fqsqhpj-hive numerical details.    mm

  A certain copper wire has a resistm (m(9mxqs3qq, b+ )j dz9sj52jlb,yfxm z,jiance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of ago hn a50g/:69y gxrpu copper wire (originally at /rug x9pag5g6: yho n0$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungs1auvv x.8tto 12xj001roi qv vten does at r.11 xv2it0 1qj u8aoxvtov0v$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance ofz a61f9krb/ bob1 va,j about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m length of household no. 1 0a2rog/8rd dl4 copper wire (usedrl r/og 80da2d in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sik-kxvx+nlk 8 pr2t93q+ pk5zs*(xqv ndes of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lyinkkq -5+9 lnq ptxrk+x *xvnz8k s(3p2vg along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resist j+8s*f:zdcypj51lb59u nc muance. If one has twice the length of the other, what is thzj 8595 uspjufd:ylc+mbc *n1e ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connect15qaaeuwyix .t by-56ed to a precision 10.00-V power supply, and a current of 0.4212 A 5 ay1 eb.5yu waxqt-6iis precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of vr;0j52 3 9ws iuh0y z.xob/t+ kancsicopper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire. o u2i krj ;y.wcai/ 0t 3+90hbnsxsz5v
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applicationsk b) 0wuf*pf4 ym3vn7;req .dm, it is important that the value of a resistance not change with temperature. For exrn.3m7w4;q0fe p y)dmv *bukf ample, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to pw lw0k01 xpb-q/sm i6produce 3.3 kW of heat when connectemw0lbps/1iqpx- 06 kwd to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V porta5.f+ytouz zup 9ak ((bble CD player that draws a maximum of 32zuo+zb.(ktfu5 y(9ap 0 mA of current?    W

  What is the maximum voltage that cacl e9w1 ri5a4 )/qmyn+hmti8 xn be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, any(9guku 48f add current through, a 75-W lightbulb connected to its propera kuf8y49d( ug source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. Cal) p-ulb6 9 p5.dy sy kufen ibb6cu-jq)/a1vo(culate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 25x a19xmflh x1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity i pmdb .,gujyep46n 86hs delivered to homes at 240 V. If you use the lightbulb in the Uni8ep6g j,yn. ub64dm phted States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is in ofub6 jwdtywg-b13 +:e perati+b u1dwf3y-w:j bg6t eon for a total of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W porc,xmm au*7gdg/;mee-vt 2 6qczh light on day ancuageve/m2qm 6 x7,td ;- gzm*d night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in ( dmjahin1-3g 0 qf2peseries as in Fig. 18–4b (igfja qe0dhp1-n(m 32Fig. 18–36). The bulb draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energy sto 9qrqp9ew4c,oy; a 9kyred in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as if hnb+3ju qb 8p6l.i;wn Fig. 18–20, can be used without blowing a 15-i3fj8n.l6; pwqbh u+ bA fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wigg d ur8/byv-4re) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power 8/br-yu 4dgv gis dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to66p-5admfcuatk sg 4- a factory through wires with total resista-64a su 5tdga6-f pmkcnce $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V1 (7 iarlti13gyk ,fuh 6zsw*o line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise b1i*ksl yo(ra,hzu i1g 3fwt6 7y no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to 5b9 e, .7ugjwarx- kzdheat a cup of water for coffee or tea. If the heater can heat 120 mL of water fr7bejru w-5kzgda9,x.om 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current in r gfjrb:1*eiw5.ygcshz.( d+a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak va *uhog+ (wqm82pavhbr :.rhc5lue is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of th4-7rx:q)zym9 b boee h6f(x ofe $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating cur /3 6-o7*tb3fxk3ihyotwhk vgrent in a 1500-W device is 5.4 A. What is the rms voltage avog3h i*6t7/hbtk ox3-kfy 3wcross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected t,xmy)9+ gxdda d*n/juscc 0 4ft0lwn6o a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp puf x qon+zszm0 :;,sn0t yj.:iump connected :x,izu+nnq 0m. z0t:j ;yfsos to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tozt(ct -*q:n4 zc skfz, a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a tiny curen*vg47: mga mrent of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 22.0 jv9g0l)sj.bgk , /xhlmV is applie ,l/)jv gs0lxhbgj.k9d to its ends. If the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmosppj4v0 d l91sp4nll2nehere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Ear; hvz+iaxr+t) m4 ;uheth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric field across an axon membrane ojbkeu1.w-tjc( m f tcy 92)pb9maq(- $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potential is detected;wx*0u 4ohs ls at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needl 4hos sxw*0;ued instead of only one?)    m/s

  Estimate how much energy ijful y4- c 5g4xt6jlqdi2h2* zs required to transmit one action potential along the axon of Example 18–15. [Hint: t l4t-y5h jg l2d 6qfxc4zuij*2he energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentialjj(zg sj tf4-;, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.0 hohi(vkrki-1.j lt( 20 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor( mt)mc 1cxwu-? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two headli4d;-s kcbm1v kghts uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 1 sdcv4- mb1kk;2-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 mfpb tlf+*d q.1 long. If it is made of iron, what mu+ 1l*.bqf tfdpst its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as xdh.7,cm8 g2x*ssjupthe reciprocal of the resistance R; that isp h7.82 xgscsu,*jmx d, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires aiwsfotr*80es* w .mi: bout 10 MW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour perw*et*ros8s:0wi. if m meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heater hv hz k;a;gju o-dxm, t,5;y3x$3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the twogru6 o kfx*a,4 lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of 6fak,gx*uor 4the original wire?

  A 1200-W hair dryer is designed for 117fq-7j0f 7j1+bgc m j3e,-hx wwgnmyu. V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it does not become so hot as to st4o (+xllb j4hfyrt-h ju9;7zg art a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more thabtjz (lrfu 4+4hxy 9h-j7o ;gln 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the eqx8nsj9:cbhaj1 ): gjuuation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy per 0 q0tkgfvwv v7f6g8k+second to 0gv6v7wv8f kfkqgt +0the interior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors made o +h-vrlo,a u5f3pby*ipe:k1b f the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of thehp+:-b5 oy1*3b,rl uaepivf k power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volum,/1csp qcnna /e $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hoohlg./xe25 htxme,bb ) ked to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its soug1b1 108y lao*vs- tk ogd*uiprce of energy. Its massgbvs1ogak0yli d1 * -*8 1upot is 1560 kg and it is powered by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a o;/ cv9k ib fbb1x0h1a8w e *rycypj;8resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Itu 7/ p-4it9-frwrtg rllinois) is designed to carry an 11-mA beam of protons travfuwt r- tpr4- t/97irgeling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord is coma xp .w3h//tx0ie9wvpper wire with a diam/9v/thx30 i.wewpa x meter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The heating elemencr9t0,ben* r (h4lton j8i4ymt is a coil of Nichrome wire. When uncoiled, the wir n48b j 9*n4rc ti(hlreyt0om,e has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltagbejo.5w7 /q9 0s8dmt rn iscz-k2c sn2e varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation,t2qnmswcd2o /i.b05 r sjns9-7 zekc8 a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household app0i eng (y.: z++u0ca uj9emaknlications. Lightbulb B is rated at 12 V and 40 W for automotivy(aji:90.una+kemu g0+eznc e applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connly 8n*-13ln iv o:mq0w wvvi+ap3 i:oject a set of appliances at 120 V, which draw 2250 W of power t pq83 3wlaw10vnvo+i::ovj ii*-y mnl otal.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside diamirk2x1w(o afz5f4 v(feter of 5.00 cm (Fig. 18–37). What is the rkofi(xf4 1f(5 aw 2rzvesistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R gy5yuv 0;ch/vv/bd.n is stretched uniformly so that its length doubles, by what factor does the p v/;vbdu cy/gy0.hv5nower dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates axl g)ttj -;j0at 0.20 A and 3.2 V. If its resistance ) ajl0x-gtjt; at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$